Molality, while being spelled and pronounced in a similar fashion to molarity, is actually more similar to mole fraction as a concentration unit.

Molality is defined as moles of solute per kilogram of solvent.

This unit of measure can be used whenever the exact amounts of both solute and solvent are critical to a property of the solution. It is more convenient for preparing solutions than a straight mole fraction.

Some constants are tabulated with units of molality for freezing point depression and boiling point elevation.